1. Field of the Invention
The present invention relates to an apparatus and method for obtaining depth-resolved spectra for the purpose of determining structure by measuring elastic scattering properties. More particularly, Fourier domain, low-coherence interferometry techniques are applied to light scattering spectroscopy. This approach permits the viewing and recovery of depth-resolved structures, as well as obtaining spectroscopic information about scattered light as a function of depth.
2. Background of the Related Art
Accurately measuring small objects or other physical phenomena is a goal that is pursued in many diverse fields of scientific endeavor. For example, in the study of cellular biology and cellular structures, light scattering spectroscopy (LSS) has received much attention recently as a means for probing cellular morphology and the diagnosing of dysplasia. The disclosures of the following references are incorporated by reference in their entirety:                Backman, V., V. Gopal, M. Kalashnikov, K. Badizadegan, R. Gurjar, A. Wax, I. Georgakoudi, M. Mueller, C. W. Boone, R. R. Dasari, and M. S. Feld, IEEE J. Sel. Top. Quantum Electron., 7(6): p. 887–893 (2001); Mourant, J. R., M. Canpolat, C. Brocker, O. Esponda-Ramos, T. M. Johnson, A. Matanock, K. Stetter, and J. P. Freyer, J. Biomed. Opt., 5(2): p. 131–137 (2000); Wax, A., C. Yang, V. Backman, K. Badizadegan, C. W. Boone, R. R. Dasari, and M. S. Feld, Biophysical Journal, 82: p. 2256–2264 (2002); Georgakoudi, I., E. E. Sheets, M. G. Müller, V. Backman, C. P. Crum, K. Badizadegan, R. R. Dasari, and M. S. Feld, Am J Obstet Gynecol, 186: p. 374–382 (2002); Backman, V., M. B. Wallace, L. T. Perelman, J. T. Arendt, R. Gurjar, M. G. Muller, Q. Zhang, G. Zonios, E. Kline, T. McGillican, S. Shapshay, T. Valdez, K. Badizadegan, J. M. Crawford, M. Fitzmaurice, S. Kabani, H. S. Levin, M. Seiler, R. R. Dasari, I. Itzkan, J. Van Dam, and M. S. Feld, Nature, 406(6791): p. 35–36 (2000); Wax, A., C. Yang, M. Mueller, R. Nines, C. W. Boone, V. E. Steele, G. D. Stoner, R. R. Dasari, and M. S. Feld, Cancer Res, (accepted for publication).        
The LSS technique examines variations in the elastic scattering properties of cell organelles to infer their sizes and other dimensional information. In order to measure cellular features in tissues and other cellular structures, it is necessary to distinguish the singly scattered light from diffuse light, which has been multiply scattered and no longer carries easily accessible information about the scattering objects. This distinction or differentiation can be accomplished in several ways, such as the application of a polarization grating, by restricting or limiting studies and analysis to weakly scattering samples, or by using modeling to remove the diffuse component (s).
As an alternative approach for selectively detecting singly scattered light from sub-surface sites, low-coherence interferometry (LCI) has also been explored as a method of LSS. Experimental results have shown that using a broadband light source and its second harmonic allows the recovery of information about elastic scattering using LCI [7].
More recently, angle-resolved LCI (a/LCI) has demonstrated the capability of obtaining structural information by examining the angular distribution of scattered light from the sample or object under examination. The a/LCI technique has been successfully applied to measuring cellular morphology and to diagnosing intraepithelial neoplasia in an animal model of carcinogenesis.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.